X86_64: Add allocation entrypoint switching for CC is_marking

Only X86_64 done so far. Use normal TLAB allocators if GC is not
marking.

Allocation speed goes up by ~8% based on perf sampling.

Without change:
1.19%: art_quick_alloc_object_region_tlab

With change:
0.63%: art_quick_alloc_object_tlab
0.47%: art_quick_alloc_object_region_tlab

Bug: 31018974
Bug: 12687968

Test: test-art-host-run-test

Change-Id: I4c4d9eb229d4ad2f41b856ba5c2958a5eb3b7ffa